Applications are represented by GIO GAppInfo objects here.
GIO has a concept of recommended and fallback applications for a
given content type. Recommended applications are those that claim
to handle the content type itself, while fallback also includes
applications that handle a more generic content type. GIO also
knows the default and last-used application for a given content
type. The GtkAppChooserWidget provides detailed control over
whether the shown list of applications should include default,
recommended or fallback applications.